Some of the best California surf breaks on Huntington Beach's 8 1/2-mile shore--home to a renovated 1906 pier, the annual U.S. Surfboard Championships, and the publicized confrontations of beachgoers and police. But the suburban residential city with both luxury beachfront homes and affordable rental housing is outgrowing the image of an aging beach town or a bedroom community. Now the county's third-largest city, Huntington Beach grew in population from 11,500 in 1965 to 178,500 in 1985 with the help of property tax and oil revenues. But an increase in new businesses and the city's now active pursuit of business development is changing the city's tax base, along with its image. Four privately owned Huntington Beach companies are among 500 named by Inc. magazine as the fastest growing in the nation, and the City Community Development Department plans to attract more. Planners see a renaissance ahead in the city's deteriorating downtown district--a $345-million mixed use development is awaiting approval--and city-sponsored redevelopment areas extend to the northeastern edge of the city. Near the Huntington Center shopping mall, a new One Pacific Plaza office center is changing the low-rise city's horizon with a mid-size skyline of towers.